Braided stents have typically been braided on a smooth mandrel. The ends of the braiding wires were typically gathered beyond an end of a braiding mandrel, and the wires where then secured, typically by tying or taping, to the mandrel end portion, after which braiding, either by hand or machine, commenced.
The braiding angle was controlled by the angle at which the stent wires were disposed over the mandrel. Many stents, however, use metallic wires which may shift or move during braiding as a result of forces imparted on the wires during the braiding. This may result in a variation of the braiding angle though the stent, in particular for stents braided with varied diameters, such as flared, flanged and/or tapered stents. Variation in the braiding angle may result in undesirable variation of radial expansion or compression forces or deployment forces of the so formed stent. Such variations may also effect the consistency of the size of the openings, e.g., cell size, across the stent.
Wire used in the fabrication of the stent is generally fed from a spool onto the mandrel. In this manner, multiple stents could be formed by feeding enough material to the mandrel during the braiding process and thereafter cutting the resulting long stent into multiple smaller stents. After braiding the long stent, the wire portions gathered beyond the mandrel end were trimmed. The trimming of such excess wire needlessly wastes material. As many early stents were braided simply with stainless steel wires, the cost of discarding this excess wire material was minimal. More recently, however, stent wires of more expensive materials, such as nitinol or composite nitinol have been used. The cost of the discarded material has become much more costly.
Thus, there is a need in the art to provide a method for braiding a stent where material costs are minimized and where variations in the stent configuration, including braiding angle, are also minimized. Further, there is a need in the art to provide a method for braiding a stent with atraumatic ends from discrete wire lengths so that the braiding angle(s) of the stent and the size and orientation of the atraumatic ends are controllably provided to produce atraumatic stents with consistency while allowing for mass production of the atraumatic stents. Moreover, there is a need optimize stent manufacturing to more tightly control stent specifications, including optimizing material control and including ability to create any specific quantity of custom stents as desired.